Extruders
For most materials Direct Drive
Ender 3 Direct Drive Kits
Less modes of failures.
Decrease acceleration
Increase nozzle size for more speed, 
EZR Extruder
Complete Kit
Software fix Ringing
https://www.youtube.com/watch?v=VK_FUvxwGxM
https://3dprinterly.com/3d-printing-ghosting-ringing-echoing-rippling-how-to-solve/
https://3dprinterly.com/how-to-get-the-perfect-jerk-acceleration-setting/
Acceleration Jerk settings
https://www.youtube.com/watch?v=Mnvj6xCzikM
Bowden vs Direct
Aluminum Direct Drive Crealit
Dual gears extruder
Double Pully Extruder
Near End Kit
BMG Dual Drive Extruder
https://www.youtube.com/watch?v=VK_FUvxwGxM
3d printed adapter plate.
 an running an E3D Titan with a pancake motor and it is working great. 
You need to take into account that it has a 
3:1 gearing so the torque it
 can apply is greater than the motor alone. 
You get the added torque at 
the cost of speed. But for an extruder, speed is not a major factor.
            
            
I run a NEMA11 with a 5:1 gearbox [www.omc-stepperonline.com],
 it has done 1.75mm filament just fine. 
Coming up I have some of the 
Sanyo 11.6mm NEMA17's (70g each) that 
I'm going to run with 4:1 gearing 
as they have greater torque out of the box than the 11.  I don't expect 
any issue.
-edit to clarify, I don't run the geared stepper into the titan, but the results are still relevant